Instructions on the Ultimaker forum post:
https://ultimaker.com/en/community/22080-fatiroberti-feeder-for-bondtech-dualdrive-175mm-cheap-kit
Updated with Bottom part for 4mm/2mm Bowdens it 'should' work with https://www.youmagine.com/designs/bowden-clip-for-1-75mm-filament-4mm-bowden-tubeCreative Commons Attribution Noncommercial Share Alike